This invention relates in general to color video monitors capable of accepting digital color input signals and particularly to a color video monitor that is capable of accepting signals formatted in different modes.
The rapid proliferation of color video monitors for use with computers having digital outputs has resulted in a number of different video color format schemes or modes, hereinafter referred to simply as formats or modes. For example, it is known to have a 16 color video format coupled with a horizontal scanning frequency of 15.75 KHz and a 64 color video format coupled with a 21.8 KHz scanning frequency. Other formats are also used and still others will certainly be provided in the future. It is also desirable to provide means for developing a monochromatic display, generally in either green or amber, in many applications to satisfy viewer's preferences. The IBM Corporation has also developed a distinctive video brown known as "IBM brown" for certain of its monitors and it is also desirable to be able to produce this video color on the CRT.
The commonly known 16 color format includes red (R), green (G) and blue (B) color signals and a common intensity (I) signal. The 64 color format has R, G and B color signals and red (r), green (g) and blue (b) individually intensity signals. The horizontal scanning frequency for the 16 color format is lower than that for the 64 color format and the polarity of the incomihg vertical synchronizing signal is used to identify the mode being used, i.e., 16 or 64 color. Additionally, it is desirable to provide the viewer with a control to adjust the overall brightness and contrast of the video display to his preference.
The monitor of the invention automatically adjusts for the color mode (in the preferred embodiment, either a 16 or 64 color format) and conditions the monitor operating circuits to function therewith. This is accomplished by means of a Programmable Read Only Memory (PROM) that has a plurality of video color inputs and functional inputs and a plurality of outputs with input addressable memory locations at which are stored binary words for supplying appropriate information to the outputs.